The present invention relates to a new and improved construction of multi-wire oxygen electrode, the reactive electrode surface of which is formed from freely exposed cross-sectional surfaces of a number of electrode wires distributed along a circle and arranged in the end surface of an especially cylindrical electrode tip formed of glass and wherein the electrode wires fused in the electrode tip are electrically coupled with a cathode wire arranged in a glass sleeve or envelope. The invention further pertains to a novel method of manufacturing the aforesaid multi-wire oxygen electrode.
In the case of oxygen electrodes the cathode- and electrode wires are generally formed of platinum and the glass sleeves or envelopes with the electrode tips of glass, for instance lead glass or the trademark glass product known as "JENAER GLAS 16 III", which practically has the same thermal coefficient of expansion as platinum and a high specific electrical resistance for such electrochemical electrodes. At the end surface of the electrode tip there are uniformly distributed along a circular periphery the reactive regions formed by the freely exposed end surfaces of the electrode wires, so that they possess the same spacing from one another. The electrode wires for reasons of measurement technology are as thin as possible, their diameter amounts to for instance 0.01 millimeters, and are relatively long and they must be fused into the electrode tip smoothly, especially free of any kinks or bends and of course without any interruptions or ruptures, and additionally, they must be in good electrical contact with the cathode wire.
Owing to these requirements and the fineness of the structure of the electrode wires it is difficult to manufacture multi-wire oxygen electrodes. The fabrication is considerably facilitated by using platinum wire encased in glass, and which can be easily handled and is obtainable with good quality. Normally for this reason, for instance for the prior art four wire-oxygen electrodes four pieces of glass encased-platinum wires are fused together in a small glass tube into an electrode tip. The individual pieces of glass encased platinum wire can be easily checked for defects prior to the fusing together and with certain care during the fusing operation there are also obtained compact electrode tips which do not contain any capillary channels and in which there are arranged, as required, the electrode wires. In order to electrically connect the electrode wires with the cathode wire there is used in this case mercury. Above the electrode tip there is provided in the small glass tube a hollow compartment or space containing mercury and into which compartment there extend the ends of the electrode wires and the cathode wire. However the use of mercury for establishing the electrical contact is associated with drawbacks, both with respect to the fabrication of the oxygen electrodes since the safety measures which are required when handling mercury necessitate an additional expenditure, as well as also during the use of the finished oxygen electrodes since the usual shaking of the electrode prior to placing such into operation is bothersome but is required to insure for a faultless contact of all electrode wires with the cathode wire. Furthermore, electrodes which no longer can be used cannot simply be thrownaway, rather must be specially handled due to the presence of the mercury. Hence, it is for these reasons that multi-wire oxygen electrodes which do not contain any mercury would be of advantage in practice. However, such oxygen electrodes formed of glass encased electrode wires cannot be economically manufactured.